What is Radii of Gyration? Application

[nicolasmarie]

I am looking a definition and application of Radii of Gyration. I want to understand this concept by looking at a 50x100 Tube withstanding wind pressure as I have drawn using Autocad. So far I do know that the greater the Radii of Gyration, the greater the rigidity of the section i.e the greatest the distance away from the centroid the most rigid is the section.

Thanks in advance.

 

[CWatters]

Not really my field but wikipedea seems to cover it.

http://en.wikipedia.org/wiki/Radius_of_gyration

In short.. if you look at the cross section of a tube all the metal is a long way from the center of area (the middle). If you compare that with a round rod having the same same cross sectional area you see that all the metal is close to the center. So they have the same cross sectional area but different Radii of Gyration.

If you try and bend the rod and tube (using wind if you like) you find the tube is stiffer even though they have same cross sectional area of metal.